A project will only have organisations indicated as co-beneficiary if they applied on behalf of a consortium.
To confirm if your organisation has applied on behalf of a consortium, please verify the Applying on behalf of a consortium checkbox in the Project Details → Project Information.
Only if this box is checked will you be able to select a co-beneficiary organisation as a sending organisation.
If the project is not indicated as Applying on behalf of a consortium and it should be, please contact your National Agency in order to request an amendment to the Grant Agreement.